The main purpose of this study is to determine the anti-viral activity of combination therapy, in treating HIV, with three investigations agents: Glaxo Wellcome 141W94 ("141", also known as the Vertex protease inhibitor); 1592U89 ("1592", a novel nucleoside analog), and DuPont Merck DMP 266, a non-nucleoside reverse transcriptase inhibitor (NNRTI). These agents will be given to subjects with partial or complete resistance to indinavir, ritonavir, saquinavir or nelfinavir as assessed by detectable viral burden despite at least 20 weeks of protease inhibitor treatment.